This application is based on Patent Application No. 2001-233926 filed Aug. 1, 2001 in Japan, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to an image processing method, a printing system and a printing apparatus, and more specifically, to a density reproduction in printing performed by using printing agents of same base color or same hue, which are different in a concentration of a coloring material included therein.
2. Description of the Related Art
Ink jet printers are known as one of the most widely used printing apparatuses. Many of such widely used printing apparatuses have recently used printing agents of different coloring material densities for the same base color or hue. For example, an ink jet printer not only uses cyan, magenta, yellow, and black inks but also uses, for cyan and magenta, light color ink composed of coloring material such as a dye or pigment having a lower concentration. This improves image quality by, for example, reducing the granularity of ink dots in a low-density portion of a printed image.
A printer of this kind performs printing using, for example, a total of six types of inks including dark and light cyan inks, dark and light magenta inks, and yellow and black inks, as described above. Accordingly, a plurality of inks are often used to represent one color, then an ink applying rate, which is an amount of ink ejected per unit area of a printing sheet, tends to be close to its maximum value determined considering the ink absorbency of the printing sheet and the like.
FIG. 1 is a diagram illustrating the applying rate of ink. More specifically, this figure shows an ink dot arrangement pattern (also referred to as an xe2x80x9cindex patternxe2x80x9d) for data on density of one color for each pixel which data are transmitted by a host apparatus such as personal computer. More specifically, the host apparatus transmits any of the nine data xe2x80x9c0xe2x80x9d to xe2x80x9c8xe2x80x9d to the printer as index data representative of the density of the pixel. The printer then forms ink dots in a pattern according to this index. Thus, the printer can achieve printing at a resolution higher than that represented by the index data.
In the figure, circles denoted by signs a and b each represent one dot composed of one ink droplet. The circles a and b both indicate ink droplets but are denoted using the different patterns for the convenience of illustration. Further, the circles a and b are arranged so as to lie partially outside square frames. This is also for the convenience of illustration. Actually, ink is ejected so that the dots are formed within the square frame. The dots are formed within the frame or so as to lie slightly partially outside the frame depending on various errors in the printer.
In FIG. 1, the 2xc3x972=4 squares shown for each of the index data xe2x80x9c0xe2x80x9d to xe2x80x9c8xe2x80x9d correspond to a print resolution for the printer, i.e. forming density of dots. This is achieved when, for example, the arrangement density of ejection openings in a printing head is the same as this dot forming density and when the frequency of ink ejecting operations performed at a certain scanning speed of the printing head is set according to this dot forming density.
The ink applying rate is said to be 100% when the printer forms one dot in the small square constituting the 2xc3x972 square. On the other hand, on the host apparatus side, when the ink applying rate is defined on the basis of pixels corresponding to the respective index data, the ink applying rate is determined by the number of dots arranged in the 2xc3x972 square for each index data shown in FIG. 1. In the following description, the ink applying rate refers to the value determined for each data corresponding to the pixels. More specifically, FIG. 1 shows an example that zero to eight ink droplets are caused to be applied on the printing sheet for each pixel in the host data, i.e. an example of index pattern formed in the case that the applying rate is 0% to 200%. In the figure, the index data xe2x80x9c0xe2x80x9d indicates white. In this case, the applying rate is 0%, and no dots are formed. With the index data xe2x80x9c1xe2x80x9d, one dot is formed and the applying rate is 25%. With the index data xe2x80x9c2xe2x80x9d, two dots are formed and the applying rate is 50%. This principle applies to the other cases, and with the index data xe2x80x9c8xe2x80x9d, eight dots are formed and the applying rate is 200%.
The index pattern shown in FIG. 1 is used, for example, for each of the six types of inks described above. This enables printing using the respective inks.
FIG. 2 is a graph showing a conventional example of the ink applying rate described above. This graph shows the ink applying rate of ink used for colors obtained by varying signal values for green, each of which is one of the colors represented by combinations of signals R, G, and B, when the colors are represented using the above described six types of inks, as well as a total applying rate corresponding to the total of these applying rates.
In FIG. 2, the numbers on a horizontal axis denotes points which are obtained by dividing the range of variations in signal values into 32 portions, which range is of hue of green and varies from white through green to black depending on variations in R, G, B signal values. A vertical axis indicates the applying rates of ink used to represent colors with the respective signal values, as well as the total applying rate. The number 1 on the vertical axis corresponds to white (signal values: R=G=B=255), and no ink of any types is used. Then, as the signal values vary from white to green (as the number increases), the density of green is increased using first the yellow ink and the light cyan ink. Furthermore, at the density (number 12) at which the color cannot be represented with only the light cyan ink, the dark cyan ink starts to be used. Subsequently, the density is increased using the light and dark cyan inks and the yellow ink until the maximum saturation or maximum density of green (number 17; signal values: R=0, G=255, and B=0) are reached. Then, at this maximum saturation point, the use of the light cyan ink is stopped. This is because dark color ink has a higher density and a wider color reproduction range than light color ink. Then, in the range with which the color represented by the signal values vary from green to black, the saturation and lightness are reduced using the light magenta ink, which is complementary color to green. In a way of this range, similarly to the case of cyan-based ink, the dark magenta ink begins to be used in addition to the light magenta ink (number 22). Subsequently, the saturation and lightness are further reduced, and for this purpose the black ink is used to make the color closer to black (number 24). For the black corresponding to the number 33 (signal values: R=G=B=0), the black, dark cyan, dark magenta, and yellow inks are all used.
In the case of representing colors varying as described above, then in the illustrated example, the total applying rate is about 220%. The maximum applying rate is determined on the basis of the ink receiving capability and ink permeation property of a printing medium, a printing speed, and the like. That is, the illustrated example indicates that the printing medium can cope with a maximum applying rate of 220%.
As shown in FIG. 2, the total applying rate reaches its maximum value of 220% when the light cyan ink is ejected at the maximum applying rate (number 13). Further, the total applying rate decreases rapidly near the maximum saturation point or maximum density point. Subsequently, the total applying rate first increases with increasing of amount of complementary color components. Then, the applying rates of the dark cyan, dark magenta and yellow inks decrease because of an increase in amount of black ink, and thus the total applying rate correspondingly decreases.
However, with the above described conventional method of performing printing using dark and light color inks, the total ink applying rate may decrease rapidly in some range. Consequently, the printed image may have a portion that is not appropriately reproduced in density, such as partly decrease in the printed density.
More specifically, as shown in FIG. 2, the light cyan ink is used until the total applying rate reaches its maximum value. Then, the dark cyan ink starts to be used in addition to the light cyan ink, and once the maximum saturation or the maximum density point (number 17) is reached, only the dark cyan ink is used. As a result, the light and dark cyan inks are quickly switched within a relatively narrow range of signal values (from number 12 to number 17). Thus, the total applying rate, including the applying rate of the yellow ink, decreases rapidly. Such a decrease in the total applying rate reduces an area factor, which is a rate of the area of the printing medium covered with ink dots, of an area printed based on gradation value data of the corresponding range. As a result, the forming density of dots in this area may decrease compared to surrounding areas or the densities of the surrounding areas increase rapidly compared to this area. Therefore, the density may be partially inappropriately reproduced.
An object of the present invention is to provide an image processing apparatus and a printing system and apparatus that enable density to be appropriately reproduced for a printing operation that uses color materials of different densities for colors of similar shades.
In the first aspect of the present invention, there is provided an image processing method for generating printing data based on an image signal, the printing data being used for a printing apparatus that performs printing on a printing medium using, for same base color, a printing agent of a first coloring material concentration and a printing agent of a second coloring material concentration lower than the first color material concentration,
wherein for a range of variations in image signal values corresponding to a variation of color from white, through a color having a maximum saturation or a maximum density of a predetermined color, to black, printing data are generated so that both the printing agent of the first coloring material concentration and the printing agent of the second coloring material concentration are used for the signal values of the color having the maximum saturation or the maximum density of the predetermined color.
In the second aspect of the present invention, there is provided an image processing method for generating printing data based on an image signal, the printing data being used for a printing apparatus that performs printing on a printing medium using, for same base color, a printing agent of a first coloring material concentration and a printing agent of a second coloring material concentration lower than the first color material concentration,
wherein for a range of variation in image signal values, printing data are generated so that
the distribution of an applying rate of the printing agent of the second coloring material concentration varies from a maximum value thereof to zero with 10 of 32 intervals into which is divided the range of variations corresponding to a variation of color from white, through a color having a maximum saturation or a maximum density of a predetermined color, to black, and
for the 10 unit intervals, a total applying rate of printing agents used has a smaller change rate than that of the applying rate of the printing agent of the second coloring material concentration.
In the third aspect of the present invention, there is provided an image processing method for generating printing data based on an image signal, the printing data being used for a printing apparatus that performs printing on a printing medium using, for same base color, a printing agent of a first coloring material concentration and a printing agent of a second coloring material concentration lower than the first color material concentration,
wherein for a range of variations in image signal values, printing data are generated so that
an applying rate of the printing agent of the second coloring material concentration varies from zero through a maximum value thereof back to zero with N/2 or more of N (an integer equal to or larger than 2) unit intervals into which is divided the range of variations corresponding to a variation of color from white, through a color having a maximum saturation or a maximum density of a predetermined color, to black, and
for the range of variations in signal values with which range the applying rate distribution of the printing agent of the second coloring material concentration varies from a maximum value thereof to zero, a total applying rate of printing agents used has a smaller change rate than that of the applying rate of the printing agent of the second coloring material concentration.
In the fourth aspect of the present invention, there is provided a printing system including a printing apparatus that performs printing on a printing medium using, for same base color, a printing agent of a first coloring material concentration and a printing agent of a second coloring material concentration lower than the first color material concentration and an image processing apparatus for generating printing data used in the printing apparatus based on an image signal,
wherein the image processing apparatus generates the printing data so that for a range of variations in image signal values corresponding to a variation of color from white, through a color having a maximum saturation or a maximum density of a predetermined color, to black, both the printing agent of the first coloring material concentration and the printing agent of the second coloring material concentration are used for the signal values of the color having the maximum saturation or the maximum density of the predetermined color.
In the fifth aspect of the present invention, there is provided a printing system including a printing apparatus that performs printing on a printing medium using, for same base color, a printing agent of a first coloring material concentration and a printing agent of a second coloring material concentration lower than the first color material concentration and an image processing apparatus for generating printing data used in the printing apparatus based on an image signal,
wherein the image processing apparatus generates the printing data so that for a range of variation in image signal values,
the distribution of an applying rate of the printing agent of the second coloring material concentration varies from a maximum value thereof to zero with 10 of 32 intervals into which is divided the range of variations corresponding to a variation of color from white, through a color having a maximum saturation or a maximum density of a predetermined color, to black, and
for the 10 unit intervals, a total applying rate of printing agents used has a smaller change rate than that of the applying rate of the printing agent of the second coloring material concentration.
In the sixth aspect of the present invention, there is provided a printing system including a printing apparatus that performs printing on a printing medium using, for same base color, a printing agent of a first coloring material concentration and a printing agent of a second coloring material concentration lower than the first color material concentration and an image processing apparatus for generating printing data used in the printing apparatus based on an image signal,
wherein the image processing apparatus generates the printing data so that for a range of variations in image signal values,
an applying rate of the printing agent of the second coloring material concentration varies from zero through a maximum value thereof back to zero with N/2 or more of N (an integer equal to or larger than 2) unit intervals into which is divided the range of variations corresponding to a variation of color from white, through a color having a maximum saturation or a maximum density of a predetermined color, to black, and
for the range of variations in signal values with which range the applying rate distribution of the printing agent of the second coloring material concentration varies from a maximum value thereof to zero, a total applying rate of printing agents used has a smaller change rate than that of the applying rate of the printing agent of the second coloring material concentration.
In the seventh aspect of the present invention, there is provided a printing apparatus that performs printing on a printing medium using, for same base color, a printing agent of a first coloring material concentration and a printing agent of a second coloring material concentration lower than the first color material concentration, based on printing data generated based on an image signal,
wherein based on the printing data generated for a range of variations in image signal values corresponding to a variation of color from white, through a color having a maximum saturation or a maximum density of a predetermined color, to black, both the printing agent of the first coloring material concentration and the printing agent of the second coloring material concentration are used for printing the color having the maximum saturation or the maximum density of the predetermined color.
In the eighth aspect of the present invention, there is provided a printing apparatus that performs printing on a printing medium using, for same base color, a printing agent of a first coloring material concentration and a printing agent of a second coloring material concentration lower than the first color material concentration, based on printing data generated based on an image signal,
wherein for a range of variation in image signal values, printing is performed so that
the distribution of an applying rate of the printing agent of the second coloring material concentration varies from a maximum value thereof to zero with 10 of 32 unit intervals into which is divided the range of variations corresponding to a variation of color from white, through a color having a maximum saturation or a maximum density of a predetermined color, to black, and
for the 10 unit intervals, a total applying rate of printing agents used has a smaller change rate than that of the applying rate of the printing agent of the second coloring material concentration.
In the ninth aspect of the present invention, there is provided a printing apparatus that performs printing on a printing medium using, for same base color, a printing agent of a first coloring material concentration and a printing agent of a second coloring material concentration lower than the first color material concentration, based on printing data generated based on an image signal,
wherein for a range of variations in image signal values, printing is performed so that
an applying rate of the printing agent of the second coloring material concentration varies from zero through a maximum value thereof back to zero with N/2 or more of N (an integer equal to or larger than 2) unit intervals into which is divided the range of variations corresponding to a variation of color from white, through a color having a maximum saturation or a maximum density of a predetermined color, to black, and
for the range of variations in signal values with which range the applying rate distribution of the printing agent of the second coloring material concentration varies from a maximum value thereof to zero, a total applying rate of printing agents used has a smaller change rate than that of the applying rate of the printing agent of the second coloring material concentration.
With the above configuration, for a range of variations in signal values of image signals, which range corresponds to a variation of color from white, through a color having a maximum saturation or a maximum density of a predetermined color, to black, both a printing agent of a first coloring material concentration and a printing agent of a second coloring material concentration lower than the first color material concentration are used in connection with a signal value for the color having the maximum saturation or the maximum density of the predetermined color. This prevents a total applying rate of a printing agent used for printing from decreasing rapidly near a maximum saturation or a maximum density point, compared to the use of only the printing agent of first coloring material concentration.
Further, for a range of variations in signal values of image signals, with 10 of 32 intervals into which is divided the range corresponding to a variations of color from white, through a color having a maximum saturation or a maximum density of a predetermined color, to black, a distribution of the applying rate of a printing agent of a second color material concentration lower than a first color material density concentration is changed from a maximum of the applying rate to zero, and with 10 unit intervals, the total applying rate of printing agents used has a smaller change rate than that of the applying rate of a printing agent of the second color material concentration. Thereby, the applying rate distribution of the printing agent of the second color material concentration varies relatively gently from its maximum value to zero with the 10 unit intervals. Furthermore, with the range from its maximum value to zero, the total applying rate varies more gently than the gently varying applying rate of the printing agent of the second coloring material concentration.
Furthermore, for a range of variations in signal values of image signals, with N/2 or more of N (an integer equal to or larger than 2) unit intervals into which is divided the range corresponding to a variation of color from white, through a color having a maximum saturation or a maximum density of a predetermined color, to black, the applying rate of a printing agent of a second coloring material concentration lower than a first coloring material concentration varies from zero through a maximum value thereof back to zero, and for variation range of a signal value in which the applying rate distribution of the printing agent of the second coloring material concentration varies from a maximum value thereof to zero, the total applying rate of printing agent used has a smaller change rate than that of the applying rate of the print agent of the second color material density. Thereby, the printing agent of the second coloring material concentration can be used with half or more of the total range of the signal value. Furthermore, with this range, the total applying rate varies more gently than that of the applying rate of the printing agent of the second coloring material concentration.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.